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Luminous Flux Conversion
Tool Description
Luminous Flux Conversion is an online luminous flux unit converter that supports mutual conversion between lumen (lm), candela steradian (cd·sr), and kilolumen (klm). Enter any value and unit to instantly view the corresponding results in all other units. Suitable for lighting design, fixture selection, light source comparison, architectural lighting standards, and more.
How to Use
- Enter a value
Enter the luminous flux value to convert in the input field, supporting integers and decimals, e.g.,
800or0.5 - Select source unit
Choose the luminous flux unit of your value from the dropdown (lm, cd·sr, klm)
- View results
Click the Convert button or press Enter, and the result area below will display the corresponding values in all units, with a copy button on the right of each result for easy use
Use Cases
- Lighting design: In indoor lighting design, you need to calculate the required luminous flux of fixtures based on different room areas and illuminance requirements. Use this tool to quickly convert between lm and klm for selecting appropriately powered fixtures
- Fixture comparison: When purchasing bulbs or fixtures, different brands may label luminous flux in different units (e.g., an LED bulb labeled 800 lm, a floodlight labeled 3 klm). Use this tool to quickly unify units for comparison
- Photometry learning: When studying basic photometry concepts, understand the relationship between luminous flux (lm) and luminous intensity (cd) — 1 lm = 1 cd·sr. Use this tool to visually verify unit conversions
Key Advantages
- Free with daily quota
This tool gives you free daily uses, enough for everyday light conversion needs. For higher volumes or more frequent use, a membership unlocks more quota.
- Local calculation
All conversions run entirely in your browser. Your input never leaves your device, keeping your data private.
- Easy to use
Just enter a value and pick a unit, then one click shows all target results. Enter key is also supported for quick conversion.
- Comprehensive units
Supports lumen (lm), candela steradian (cd·sr), kilolumen (klm) and other common luminous flux units, covering lighting selection and engineering calculation.
- High precision
Uses exact conversion factors with double-precision floating-point math, keeping enough decimals for professional and daily needs.
- Cross-platform
The responsive layout works smoothly on phone, tablet and desktop, so you can convert luminous flux anytime, anywhere.
Luminous Flux Unit Conversion Relationships
The following shows the conversion relationships between luminous flux units, with lumen (lm) as the base unit:
| Unit Name | Abbr. | Conversion Relationship | Equivalent lm |
|---|---|---|---|
| Lumen | lm | 1 lm（基准单位） | 1 |
| Candela Steradian | cd·sr | 1 cd·sr = 1 lm | 1 |
| Kilolumen | klm | 1 klm = 1,000 lm | 1,000 |
Common Light Source Luminous Flux Reference
The following shows the luminous flux ranges of common light sources in daily life for reference comparison:
| Light Source Type | Luminous Flux |
|---|---|
| Night light / Indicator light | ~10 lm |
| Standard LED bulb (5-7W) | 450 ~ 800 lm |
| LED bulb (10-15W, replaces 60W incandescent) | 800 ~ 1,600 lm |
| LED tube / Ceiling light (20-30W) | 1,000 ~ 3,000 lm |
| LED floodlight / High bay light (30-80W) | 3,000 ~ 8,000 lm |
| Street light / Plaza lighting (100-300W) | 10,000 ~ 30,000 lm |
| Professional stadium metal halide lamp (400W) | ~35,000 lm |
Difference Between Luminous Flux and Illuminance
Luminous Flux and Illuminance are two distinct but related concepts in photometry. Luminous flux measures the total amount of visible light emitted by a source, with the unit of lumen (lm), describing "how much light the source emits in total"; illuminance measures the luminous flux received per unit area, with the unit of lux (lx = lm/m²), describing "how bright a certain area is."
The relationship between the two is: Illuminance (lx) = Luminous flux (lm) ÷ Area (m²). For example, a 1,000 lm light source illuminating a 10 m² room produces an average illuminance of about 100 lx. Candela steradian (cd·sr) is another expression of luminous flux: a point source with luminous intensity of 1 cd radiating within a solid angle of 1 steradian (sr) produces a luminous flux of 1 lm, i.e., 1 lm = 1 cd·sr. This relationship derives from the definition of luminous intensity (candela).
FAQ
Lumen (symbol lm) is the standard SI unit of luminous flux, representing the total amount of visible light emitted by a source. 1 lumen is defined as the luminous flux radiated by a uniform point source of 1 candela (cd) luminous intensity within a solid angle of 1 steradian (sr), i.e., 1 lm = 1 cd·sr. The lumen is the core metric for evaluating light source brightness — the larger the lumen rating on a bulb, the brighter it is. For example, an 800 lm LED bulb has brightness equivalent to a traditional 60W incandescent bulb.
1 lm = 1 cd·sr, the two are numerically equivalent. The lumen is the SI derived unit of luminous flux, and candela steradian is its definitional expression. The candela (cd) is the unit of luminous intensity (one of the seven SI base units), and the steradian (sr) is the unit of solid angle. For example, a uniform point source with luminous intensity of 100 cd radiates 100 lm of luminous flux within a solid angle of 1 sr. In engineering practice, lumen (lm) is typically used directly and rarely written as cd·sr.
1 klm = 1,000 lm, 1 lm = 0.001 klm. The kilolumen is a thousand-fold unit of the lumen, used for expressing larger luminous flux values relevant to high-power fixtures and industrial lighting scenarios. For example, an LED floodlight with 3,000 lm can be written as 3 klm; a sports stadium lighting system can have a total luminous flux of hundreds of klm. In everyday household scenarios, lm is usually sufficient.
No. Wattage (W) is a power unit indicating the electrical energy consumed by a fixture; lumen (lm) is a luminous flux unit indicating the total visible light emitted. The two are related through efficacy (lm/W): Luminous flux (lm) = Power (W) × Efficacy (lm/W). Different light sources have vastly different efficacies: traditional incandescent bulbs have about 10-15 lm/W, while LED bulbs can reach 80-120 lm/W. Therefore, a 10W LED bulb (about 800 lm) is brighter than a 60W incandescent bulb (about 700 lm). When purchasing fixtures, focus on the lumen rating rather than wattage.
No. All conversion calculations are performed entirely in your browser locally using pure JavaScript math. Your input data never leaves your device, so please feel free to use it.
This tool uses JavaScript double-precision floating-point numbers (64-bit IEEE 754) for calculations, which is sufficiently accurate for most everyday scenarios. The lumen and candela steradian have a definitional equivalence (1 lm = 1 cd·sr), and the kilolumen follows a strict decimal thousand-fold relationship with the lumen (1 klm = 1,000 lm) with no approximate conversions, so results are precise within floating-point range. Up to 6 significant decimal places are retained, with excess digits automatically truncated.
Very simple.Enter the luminous flux value to convert, select its unit from the dropdown, click the Convert button or press Enter, and the result area will immediately list the converted values for all units (lm, cd·sr, klm). Each result has a copy button on the right to copy that value individually.
3 units in total.They include lumen (lm), candela steradian (cd·sr, definitionally equivalent to lm, 1 lm = 1 cd·sr), and kilolumen (klm, 1 klm = 1,000 lm), covering daily lighting and engineering calculation needs.
No registration needed.This is a free online tool that works as soon as you open the page, without login or account binding. We provide free daily usage quota; light daily conversion needs can be met at zero cost, while higher quotas or more frequent use can be unlocked by becoming a member.
Yes.The page is responsive and works properly on phones, tablets, and desktop browsers. Conversion on mobile is also done locally, so you can use it anytime, anywhere without worrying about network transmission.
Different meanings.Luminous flux (lumen) measures the total visible light emitted by a source, a "total amount" concept; luminous intensity (candela, cd) measures the source''s emission ability in a specific direction, a "direction" concept. The relationship is: luminous flux = luminous intensity × solid angle (lm = cd·sr). An isotropic point source with 1 cd intensity has a total luminous flux of 4π ≈ 12.57 lm.
You will be prompted to re-enter.When the input is empty or non-numeric, the tool shows prompts like "Please enter a value" or "Please enter a valid number" and does not perform conversion. Only regular numeric values (integers, decimals, and scientific notation) are supported; letters, unit symbols, and other non-numeric content are not accepted. Please confirm the input is a pure number and try again.
Content last updated：2026-07-17
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